This is the result of getting jerked around by politicians every few years. America got to the moon because it was something everyone could agree upon that would stick it to the Ruskies!
After doing the bulk r&d for the Apollo project, the budget sort of tapered off
It's like every President since Kennedy felt they needed to give NASA some long term objective just to have the following Presidency give them something else, and have both House and Senate subcommittees give their two cents on objectives and funding.
It's just a recipe for the bullshit you see right now.